The cellular RNA decay machinery routinely polices the cell and effectively removes unwanted RNAs. We have recently discovered that alphaviruses, including VEE, possess specific RNA stabilizing elements in their 3'UTR that recruit a cellular factor and block the deadenylation/decay of viral transcripts, thereby promoting an efficient and productive infection. Based on these data, we hypothesize that many if not all RNA viruses that encode capped and polyadenylated transcripts have evolved mechanisms to selectively suppress the cellular mRNA decay machinery as a prerequisite for efficient virus gene expression. The goal of Aim I of this proposal is to test this hypothesis by assessing whether we can extend our observations on viral suppression of the cellular RNA deadenylation/decay machinery to additional alphaviruses (WEE and EEE) as well as negative sense RNA viruses (Ebola, Marburg and Nipah). In addition to expanding our knowledge of molecular host-virus interactions, these studies will also test whether these agents employ a similar strategy as the alphaviruses for mediating viral RNA stability. If these RNA viruses use a single (as preliminary data indicate is the case for alphaviruses) or limited number of strategies to suppress the cellular mRNA decay machinery, this represents a novel and attractive target for antiviral therapeutics. To this end, the goal of Aim 2 is to optimize our established in vitro assays for measuring viral mRNA stability to allow for the rapid and effective screening of chemical compound libraries. The final aim of this proposal is to perform a chemical library screen to identify and validate candidate lead compounds that overcome viral suppression of the cellular RNA decay machinery. These compounds would represent attractive candidates for further development as antiviral therapeutics that may very well have a broad spectrum activity against a variety of viruses of biodefense significance. This research project fits within the RMRCE Integrated Research Focus on Viral Therapeutics, and will interact directly with RPs 3.1, 3.2, 3.5, 3.7 and 3.8, and utilize the resources of Core E. The goals of this project should add significant expertise to and synergize well with the RMRCE Viral Therapeutics Focus Group, particularly due to the innovative basic virology questions being asked and the novel approach to develop antivirals that could target multiple families of RNA viruses of interest to the Group.